1. Field of the invention
The present invention relates to an automatic paper feed device for use in electrophotographic copying machines, printers, or the like.
2. Description of the Prior Art
In the prior automatic paper feed devices, copying sheets stacked on a support plate in a paper feed cassette are pushed up to a predetermined level by a motor or a spring as a driving source so that the upper surface of the sheet stack is held in pressing contact with a paper feed roller. Subsequently, upper sheets are fed from the paper feed cassette toward a nip portion between another paper feed roller located downstream of said paper feed roller with respect to a paper feeding direction (hereinafter, this paper feed roller and the paper feed roller in pressing contact with the upper surface of the sheet stack are respectively referred to second and first paper feed rollers) and a separating roller in pressing contact with the second paper feed roller by the rotation of the first paper feed roller. At this time, the separating roller rotates in a direction opposed to the paper feeding direction for preventing a plurality of sheets from being fed simultaneously into the copying machine. As a result, only an uppermost sheet is fed in a transfer section.
However, the automatic paper feed device of this type is relatively large and expensive due to the fact that a pushing mechanism is required for pushing up a support plate on which the sheets are stacked.
Further, there arises a problem in that the pressure between the upper surface of the sheet stack and the first paper feed roller is not uniformly maintained because the pushing up of the support plate is intermittently carried out while the height of the upper surface of the sheet stack is detected.